(i) Field of the Invention
This invention relates to a connector for electrodes. More particularly, it relates to an electrode clip for the connection of a lead cable to an electrode which is secured to a human body.
(ii) Description of the Prior Art
In order to ascertain electrical phenomena arising from physiological functioning, for example electrocardiographic data associated with the functioning of the heart, e.g. in patient monitoring uses, it is necessary to apply sensory devices (known as electrodes) to the skin. The electrodes may be applied to the skin by a suction cup, aided by an electrically conductive cream, or they may be glued or taped to the patient's body. The electrode may be provided with a male pin or male snap fastener. Traditionally, the female portion of the snap fastener was intended mechanically to couple to the male portion. Several different types of cable fasteners have been used to couple electrical impulses from the electrode on a patient's body to a cable connected to an electrocardiograph or other monitoring device. It is important that a good connection be made by the electrode clip between the electrode and the lead cable.
Many deficiencies exist in such cable fasteners. For example, it was found that in many instances, the resulting electrical connection, however, was not noise-free and fatigued easily, causing loose connections. Additionally, since it was connected by pressing downward on the patient, a painfully hard push was often necessary to make a good connection. This type of snap fastener though simple and inexpensive to produce was difficult to repair.
One type of fastener which was developed to attempt to solve this problem was a hairpin and turn-cam fastener. This type of fastener made a good electrical connection when new and allowed simple application without pressing upon sensitive areas of the patient. The joint between cable and fastener was by a tubular solderless connector which was crimped on the fastener and the cable, and then covered with a shrink tubing. However, this fastener suffered many deficiencies. Unfortunately the fastener was expensive to make. It offered very little strain relief, and physically fatigued early in life, thereby causing loose connections. The electrical contact surface was only four pin point surfaces, which wore away very quickly. The length of the connector provided leverage which, when lifting the cable, often pried the connector off the snap. Because shielded wire cables work best when the exposed matellic fastenings were as small as possible, the length of this type of fastener was much too great to enhance the benefits of shielded cable. Also, whenever a patient rolled upon this type of fastener, he would likely receive a discomforting jab from its end, or cause the fastener to come off the electrode.
In an attempt to solve this problem, the cable fastener for electrocardiograph electrodes disclosed in U.S. Pat. No. 3,829,826 issued Aug. 13, 1974 to D. M. Brown et al was provided. In that cable fastener, there was included a metal bracket and a spring wire joined together. The metal bracket had a clearance hole which fit over the male snaps and had an offset to allow connections to cupmounted snaps. The spring wire provided mechanical retention, and by holding the bracket in contact with the snap, a durable electrical connection. A partial loop on the spring wire formed a finger pad for engaging and disengaging the fastener from the snap. The cable fastener mated with the male snap of an electrocardiograph electrode, for example, as it was mounted on a flat surface or seated in a cup depression. While this cable fastener was successful when new, as the spring became less resilient during use, it became less effective. On the other hand, if the spring were made strong initially, it would be more difficult to use.
In a second solution to this problem, that provided by U.S. Pat. No. 3,895,635 issued July 22, 1975 to G. F. Justus et al, a connector was provided which had a non-conductive body having one end of a cable located therein, carrying an electrical contact plate against which a stud of an electrode was locked by a non-conductive cam lever pivotally mounted on the body portion.
In a third solution, that provided by U.S. Pat. No. 4,026,278 issued May 31, 1977 to J. R. Ricketts et al, the electrode stud was inserted in a keyway hole in a connector secured electrically to the end of a cable, and held in place by a sprung back-up plate.
These latter two solutions, however, suffer the practical deficiency that in securing the connector to the electrode stud some pressure would be applied to the electrode, and thus to the human body. In many instances, this pressure against the human body is undesirable.